1. Field of the Invention
The invention generally relates to an optical apparatus, and more particularly, to a lens module and an image apparatus.
2. Description of Related Art
Along with the increasing popularity of demand on the surveillance under night and low-light environments, video cameras with 24-hours surveillance function are widespread used. In general speaking, a conventional video camera uses a light-filter for switching the 24-hours surveillance modes. In more details, when an object to be shot is under an environment with adequate luminance, a light-filter would be put down to block infrared light from entering the photosensitive component. On the other hand, when an object to be shot is under an environment with insufficient luminance, an infrared light source of the video camera would be turned on to emit infrared light onto the object to be shot. At the time, the light-filter is disabled so that the infrared light reflected by the object to be shot can reach at the photosensitive component for imaging.
In the application practice however, the images captured during day normally are clear, while the images captured during night (in infrared mode) are fuzzy. The different results are caused by a too large difference between visible light and infrared light in wavelength. In more details, after the visible light and the infrared light pass through a lens module of the video camera, due to the two focal planes of the above-mentioned two lights are apart quite far from each other; in addition, due to the cost consideration, most of the commercial video cameras for surveillance are not equipped with auto-focusing function. Under such circumstances, how to design an appropriate lens module of video cameras able to capture images with good quality at day and night becomes one of important projects to solve the above-mentioned problem by the relevant developers.
U.S. Pat. No. 7,417,802 discloses a lens module including a first lens group, a second lens group, a third lens group, a fourth lens group and a fifth lens group, in which the first, the second, the third, the fourth and the fifth lens groups have positive refractive-power, negative refractive-power, positive refractive-power, positive refractive-power and positive refractive-power, respectively. U.S. Pat. No. 7,369,313 discloses a zoom lens for a video camera. The zoom lens includes a first lens group with positive refractive-power, a second lens group with negative refractive-power, a third lens group with positive refractive-power, a fourth lens group with positive refractive-power and a fifth lens group with positive refractive-power. The fourth lens group and the fifth lens group herein respectively have an aspheric lens. In addition, U.S. Pat. Nos. 7,227,693, 6,738,196, 6,870,689 and 6,989,940 disclose several types of projection lenses. U.S. Pat. Nos. 5,299,064, 5,414,562, 5,548,445 and 5,659,426 also disclose a projection lenses including multiple lens groups.